1. Field of the Invention
The present invention relates to a communication method, control station, and communication apparatus which are used for a communication system.
2. Description of the Related Art
According to the infrastructure mode defined in IEEE802.11, a communication apparatus serving as a base station accommodates a plurality of wireless terminals serving as terminal stations to construct a network.
FIG. 1A is a view showing the system configuration of the infrastructure mode. FIG. 1B is a view showing the header formats of a management frame and data frame which are exchanged. In this case, when a base station accommodates a terminal station, the terminal station transmits a management frame containing a body format called an association request to the base station. In response to this frame, the base station returns a management frame containing a body format called an association response to the terminal station. When the terminal station stops being accommodated by the base station, the terminal station transmits a management frame containing a body format called disassociation to the base station.
According to the infrastructure mode in IEEE802.11, even terminal stations in the same wireless LAN system transmit/receive data between them through a base station, and hence high efficiency cannot always be achieved in terms of the utilization efficiency of frequencies and communication rate.
Under such situations, IEEE802.11e has proposed a technique of establishing a direct link to allow terminal stations to directly transmit/receive data between them after reaching an agreement through a base station.
FIG. 2A is a view showing a control process (control function) for direct link establishment. FIG. 2B is a view showing the body formats of management frames to be exchanged. This control process for direct link establishment is called DLS (Direct Link Set-up). Management frames (bodies) used in this DLS include a DLS request and a DLS response. A terminal station which is to establish a direct link transmits this DLS request to a base station or the base station transfers the DLS request to a partner terminal station of a direct link. In response to this request, the partner terminal station returns a DLS response to the base station, or the base station transfers it to the terminal station (which has transmitted the DLS request to the base station) which has started DLS. Note that DLS is defined as an option in IEEE802.11e.
There is proposed a technique of suitably using the above direct link by making a transmission station use the direct link when transmitting real-time data, and by making the transmission station use a route via a base station when transmitting another type of data. See, for example, patent reference 1: US 2004240405A1 (Japanese Patent Application Laid-Open No. 2004-363645).
IEEE802.11e has proposed a plurality of extension techniques for securing communication quality (QoS) in addition to the above direct link for improving the utilization efficiency of frequencies and communication rate. According to one of these techniques, a terminal station applies to a base station for information about the flow (traffic stream) of data which the self-station will transmit or receive, and the base station performs traffic control for the overall network on the basis of the information applied from each terminal station. More specifically, traffic control is performed to determine whether to permit data transmission/reception or decide a band assignment time (frequency utilization time).
FIG. 3A is a view showing a control process for QoS securement. FIG. 3B is a view showing the body formats of management frames to be exchanged. This management frame includes an ADDTS request and an ADDTS response. The ADDTS request frame is a frame which is transmitted by a terminal station which wants to secure QoS in data transmission/reception to a base station. The ADDTS response frame is a frame which the base station returns as a response to the terminal station which has transmitted the ADDTS request. The body format of a management frame further comprises an information element called an element, in which information about the flow of data is written. FIGS. 4 and 5 respectively show a traffic specification (TSPEC) element and a traffic classification (TCLAS) element of such elements.
Patent reference 2: U.S. Pat. No. 5,621,732A1 (Japanese Patent Application Laid-Open No. 7-288542), patent reference 3: Japanese Patent Application Laid-Open No. 2001-045027, and patent reference 4: Japanese Patent Application Laid-Open No. 2004-320396 disclose techniques of switching between communication via a base station and direct communication between terminal stations.
According to conventional techniques including IEEE802.11e, control for switching between data transmission/reception via a base station and direct data transmission/reception between terminal stations is independent of control for QoS securement, and do not synchronize with each other. Note that control for QoS securement includes control concerning the application of traffic by a terminal station and traffic control by a base station based on the application.
Assume that when QoS is secured for data transmission/reception while the data transmission/reception is performed via a base station, switching control is performed to perform direct data transmission/reception. This control, however, does not synchronize with control for QoS securement for data transmission/reception after the switching operation.
Furthermore, if transmission terminal stations and reception terminal stations each select data transmission/reception via a base station and apply to the base station for QoS securement concerning the data transmission/reception, the total frequency band of the network exceeds the threshold. The base station therefore does not permit this application, resulting in failure to secure QoS. The traffic in direct data transmission/reception is half that in data transmission/reception via a base station. Therefore, selecting direct data transmission/reception may make it possible to secure QoS.